I have not printed in at least a very long time, but I still have those chemicals sitting around. I think fixer lasts longer than developer, and stop is just vinegar. What are the results when using old chemicals.

On the flip side, how well does it work to mix a small batch of whatever, using part of a package of dry chemical? I know it is a solid mixture and, as such, may not be homogeneous, so one batch may be different from the next, but in practical terms, what's the result?

I think you're correct about the relative storage life of developer, stop, and fixer. When developer starts to look like maple syrup it's time to toss it. Stop bath concentrate seems to last forever; I have some that's at least 20 years old and it still seems to be alive. Fixer probably falls somewhere in between, but I've never seen any data on longevity; it's best not to tempt fate, though, because an improperly fixed photo is a chemical time bomb which is bound to shorten the life of, and ultimately destroy, the image on films and papers, especially the latter, while contaminating everything around it.

Come to think of it, Kodak used to provide data on the storage life of these materials in their Darkroom Data Guides, IIRC. I think a useful rule of thumb is: If in doubt, toss it out. I once read in a photo mag some advice on extending the life of working solutions of bottled chemicals: exhale into the bottle several times and immediately put the lid on, tight. The idea is to deposit a layer of CO2 on the surface of the chemical so it wouldn't oxidize as rapidly. I used to breathe out into a soda straw inserted into the neck of the bottle. Seemed to do the trick.

Kodak always advised against what you are proposing to do, and for the very reasons you give: lack of homogeneity in the powdered mix. Therefore I never tried it, so I can't help you there.

Another way to slow down the oxidization of developers in storage is to use one of those "Canned Air" dust blower products such as "Dust Off", they are a heavy, inert propellant gas, not compressed air. I have been able to store D-76 and Dektol for about six months using this method, but it does take a trained & sensitive ear to tell when you have displaced all the air in the bottle with the gas.

I just finished a twenty-year old bottle of HC-110, which was not even factory sealed throughout its storage (it probably got used once or twice in the late eighties, and was then shelved when I switched to T-Max, to be unearthed last year when I ran out of T-Max 9x12) - no difference to the new bottle i have now.

Not everything is internally inert, though - some stuff will destroy itself over time. I've had liquid fixers and colour chemistry which were out of spec way before the expiration date.

I tried mixing up some old dektol powder. It was probably 15 years old when I opened it the powder was a dark tan. In mixed up like mahogany wood stain.

It developed prints and since all I was doing was making prints from my daughter's pinhole camera for her 4th grade since project, it was good enough, I ran about a dozen 4x5s through a quart. But I didn't save any of it._________________"In order to invent, you need a good imagination and a lot of junk" Thomas Edison